Computed Tomography System and Patient Table Comprising a Contactless Transfer of Electrical Signals

ABSTRACT

The invention relates to a computer tomography installation having contactless data signal transmission. The device comprises at least one longitudinally slit coaxial conductor element ( 1 ), at least one high-frequency transmitting unit ( 3 ), which feeds into the conductor element ( 1 ) a high-frequency carrier signal modulated with a data signal to be transmitted, at least one longitudinally slit coaxial coupling conductor element ( 2 ), which is designed to receive the emitted modulated high-frequency carrier signal ( 21 ) from the near field of the conductor element ( 1 ), and at least one high-frequency receiving unit ( 4 ), which is electrically connected to the coupling conductor element ( 2 ) and is designed to extract the data signal from the received modulated high-frequency carrier signal, wherein the conductor element ( 1 ) and the coupling conductor element ( 2 ) are arranged in such a way that the conductor element and the coupling conductor element can be moved in relation to each other. The conductor element ( 1 ) is arranged on a rotatable gantry part ( 12 ), and the coupling conductor element is arranged on a stationary gantry part ( 13 ). The invention further relates to a patient table having such data transmission between moving parts.

FIELD OF THE INVENTION

The invention relates to a computed tomography system and a patienttable with a contactless transfer of electrical signals between unitsthat are movable relative to one another.

BACKGROUND OF THE INVENTION

In many medical engineering applications, electrical signals or datamust be transferred from a moving medical engineering system part to amedical engineering system part at rest, and vice versa.

A preferred field of application of the present invention relates to thedata transfer between the rotating part and the stationary part of acomputed tomography system. During operation of the computed tomographysystem, the data acquired by the x-ray detectors must be transferredfrom the rotating part to the stationary part of the computed tomographysystem in order to be processed further there. Here, large amounts ofdata should be transferred within a short period of time.

Many currently available computed tomography systems use a contactless“slip ring” system for data transfer, as is known from e.g. the patentdocument U.S. Pat. No. 5,140,696 A. The data transfer system describedtherein comprises a transmission unit at the rotating part and areception unit at the stationary part. The transmission unit has atleast one radiofrequency line connected to a transmitter as atransmission antenna, which is arranged at the circumference of therotating part of a rotating frame. The reception unit comprises areceiver and at least one reception antenna connected to the receiver,said reception antenna being formed by a short portion of aradiofrequency line. During operation of the computed tomography system,the transmission antenna moves past the reception antenna at a shortdistance therefrom, said reception antenna being fastened to thestationary part, and so the signals propagating on the transmittingradiofrequency line couple into the reception antenna via the nearfield.

The laid-open application DE 102 06 160 A1 discloses such a signaltransfer between moving parts, wherein the radiofrequency line isembodied as a strip line with a dielectric.

SUMMARY OF THE INVENTION

It is an object of the invention to specify a computed tomography systemand a patient table, which enable an electrical data transfer with ahigh data transfer capacity and little far field interference.

In accordance with the invention, the stated problem is solved by thecomputed tomography system and the patient table of the independentpatent claims. Advantageous developments are specified in the dependentclaims.

According to the invention, a contactless signal transfer is carried outbetween parts of a computed tomography system or of a patient table,which move relative to one another, by way of longitudinally slitcoaxial conductor elements, so called coaxial conductors. The datasignal to be transferred is modulated onto a radiofrequency carrier. Thecontactless transfer then takes place on a narrowband (modulationbandwidth up to approximately 30% of the radiofrequency carrierfrequency) by means of the conduction coupler structure with thelongitudinally slit coaxial build. The transfer function of the couplerstructure itself is broadband with a corresponding frequency response(high-pass behavior). A coaxial line (e.g. the transmission coupler)covers the whole displacement range, the circle circumference in thecase of rotating parts. A second short coaxial line (e.g. the receptioncoupler) decouples the modulated radiofrequency carrier signal over thelength thereof. The length of the coupling path is determined by thecarrier frequency and the modulation bandwidth.

The invention claims a computed tomography system with a contactlessdata signal transfer, comprising

-   -   at least one longitudinally slit coaxial conductor element,    -   at least one radiofrequency transmission unit which feeds a        radiofrequency carrier signal, modulated with a data signal to        be transferred, into the conductor element,    -   at least one longitudinally slit coaxial coupling conductor        element which is embodied to receive the emitted modulated        radiofrequency carrier signal from the near field of the        conductor element, and    -   at least one radiofrequency reception unit which is electrically        connected to the coupling conductor element and embodied to        extract the data signal from the received modulated        radiofrequency carrier signal,    -   wherein the coaxial conductor element is arranged on a rotating        or stationary gantry part and the coupling conductor element is        correspondingly arranged on the stationary or rotating gantry        part.

On account of the structural properties of the longitudinally slitcoaxial lines, the invention offers an excellent behavior in respect ofthe far-field damping, leading to a high stability and a very lowemission of the modulated signal. The data transfer is suitable, inparticular, for transfer in the single-digit and two-digit gigahertzrange. The conduction coupler can be implemented in a cost-effectivemanner from a coaxial line by partial skinning or by an insulated innerconductor, embedded in a groove, with a defined wave impedance.

In a development of the invention, the frequency of the radiofrequencycarrier signal can be greater than 10 GHz. Preferably, a transfer can becarried out in the K and Ka band between 18 and 35 GHz. Higherfrequencies up to 60 GHz are possible, but lead to reduction in thecoaxial cross section.

In a further embodiment, the device comprises a first carrier element,in which the coaxial conductor element is formed.

In a further embodiment, the first carrier element can be made of metaland form a first outer conductor of the coaxial conductor element. Thecross section of the first carrier element is preferably rectangular anda first inner conductor is arranged in a groove of the first carrierelement.

In a development, the device comprises a second carrier element, inwhich the coaxial coupling conductor element is formed.

In a further development, the second carrier element is made of metaland forms a second outer conductor of the coaxial coupling conductorelement. The cross section of the second carrier element is preferablyrectangular and a second inner conductor is arranged in a groove of thefirst carrier element.

Moreover, the invention claims a patient table with a coaxialarrangement as described above for the data signal transfer betweenparts moving in a translational manner.

Further peculiarities and advantages of the invention will become clearfrom the following explanations of an exemplary embodiment based onschematic drawings.

In detail:

FIG. 1 shows a cross section through a coaxial conductor element,

FIG. 2 shows a cross section through a device with a coaxial conductorelement and a coaxial coupling conductor element,

FIG. 3 shows a block diagram of a device with a rotatable coaxialconductor element,

FIG. 4 shows a block diagram of a device with a rotatable segmentedcoaxial conductor element,

FIG. 5 shows a block diagram of a device with a coaxial conductorelement displaceable in a translational manner,

FIG. 6 shows a block diagram of a device with a stationary coaxialconductor element and

FIG. 7 shows a computed tomography system.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

FIG. 1 shows cross sections through a longitudinally slit coaxialconductor element 1. The cross section A) shows a coaxial cable and thecross section B) shows a coaxial cable, in which the outer conductor wasremoved and which was inserted into a milled groove. The longitudinalslit can have a continuous or periodically spaced apart embodiment. Theconductor element 1 comprises a first inner conductor 9 and a firstouter conductor 8. A dielectric 5, which fixes the first inner conductor9 coaxially in relation to the first outer conductor 8, is situatedbetween the first outer conductor 8 and the first inner conductor 9. Thefirst outer conductor 8 is open toward the top, i.e. slit open. Anelectric wave guided in the conductor element 1 can partially escapethrough the forming gap. The arising electric field is represented bythe field lines 21. In cross section B), the dielectric does notcompletely fill the milled groove.

FIG. 2 shows what happens if a longitudinally slit coaxial couplingconductor element 2 is brought into the near field of the slit coaxialconductor element 1. Electric energy from the near field couples intothe coupling conductor element 2, which is e.g. also a coaxial cable.The electromagnetic field is represented by the field lines 21 thereof.

FIG. 2 shows a cross section through the conductor element 1 and thecoupling conductor element 2 arranged at a distance therefrom by the airgap 20. The conductor element 1 comprises an electrically conductivefirst carrier element 6, which forms the first outer conductor 8. Thefirst inner conductor 9 with the dielectric 5 is pressed into the firstcarrier element 6. The coupling conductor element 2 comprises anelectrically conductive second carrier element 7, which forms the secondouter conductor 10. The second inner conductor 11 with the dielectric 5is pressed into the second carrier element 7. The air gap 20 is only afew millimeters wide.

The electrically conductive carrier elements 6 and 7 lying just over oneanother act in a capacitive manner and form a short circuit for highfrequencies. Signal transfer is only possible between the first innerconductor 9 and the second inner conductor 11.

The electric conductor element 1 and electric coupling conductor element2 have e.g. an external conductor 8, 10 diameter of approximately 5.5 mmand an internal conductor 9, 11 diameter of approximately 1.5 mm. By wayof example, the carrier elements 6, 7 are made of copper and the innerconductors 9, 11 are made of silver-coated copper. By way of example,the dielectric 5 is made of PTFE. Transfers with a carrier frequency upto 35 GHz are possible therewith. The coaxial cross section needs to bereduced for higher frequencies in order to keep the coaxial conductorfree from modes. As a result, there is also reduction in the possiblespacing for the coupler structure.

FIG. 3 shows a block diagram of a device with a rotatable coaxialconductor element 1. A radiofrequency carrier signal modulated by thedata signal is fed into the conductor element 1 at the first end thereofby means of the radiofrequency transmission unit 3. The conductorelement 1 has an embodiment in accordance with FIG. 2 and is provided atthe second end thereof with a termination 19, for example a lossy lineor a terminating resistance, for a reflection-free termination. Theconductor element 1 is rotatably mounted in the direction of rotation22.

Two coupling conductor elements 2, embodied in accordance with FIG. 2,are arranged opposite one another along the circumference of theconductor element 1 for the purposes of decoupling the radiofrequencycarrier signal from the first conductor element 1. The couplingconductor element 2 is preferably a few wavelengths (a few cm) long andterminated by a termination 19 at the first end thereof. Aradiofrequency reception unit 4 is connected at the second end thereofand receives and demodulates the decoupled radiofrequency carriersignal.

Optionally, it is also possible for the coupling conductor element 2 tobe arranged in a rotatable manner and the conductor element 1 to bearranged in a stationary manner.

FIG. 4 shows a block diagram of a device with a rotatable coaxialconductor element 1 divided into two segments of equal length. Aradiofrequency carrier signal modulated by the data signal is fed intoboth conductor elements 1 at the first ends thereof by means of theradiofrequency transmission unit 3. The conductor elements 1 areembodied in accordance with FIG. 2 and provided at the second endsthereof with a termination 19 for a reflection-free termination. Theconductor elements 1 are rotatably mounted in the direction of rotation22.

One coupling conductor element 2, embodied in accordance with FIG. 2, isarranged along the circumference of the conductor elements 1 for thepurposes of decoupling the radiofrequency carrier signal from the firstconductor element 1. The coupling conductor element 2 is preferably afew wavelengths (a few cm) long and terminated by a termination 19 atthe first end thereof. A radiofrequency reception unit 4 is connected atthe second end thereof and receives and demodulates the decoupledradiofrequency carrier signal.

Optionally, it is also possible for the coupling conductor element 2 tobe arranged in a rotatable manner and the conductor element 1 to bearranged in a stationary manner.

FIG. 5 shows a block diagram of a device with a translationallydisplaceable coaxial conductor element 1. A radiofrequency carriersignal modulated by the data signal is fed into the conductor element 1at the first end thereof by means of the radiofrequency transmissionunit 3. The conductor element 1 has an embodiment in accordance withFIG. 2 and is provided at the second end thereof with a termination 19for a reflection-free termination. The conductor element 1 isdisplaceably mounted in the direction of movement 23.

One coupling conductor element 2, embodied in accordance with FIG. 2, isarranged along the conductor element 1 for the purposes of decouplingthe radiofrequency carrier signal from the first conductor element 1.The coupling conductor element 2 is preferably a few wavelengths (a fewcm) long and terminated by a termination 19 at the first end thereof. Aradiofrequency reception unit 4 is connected at the second end thereofand receives and demodulates the decoupled radiofrequency carriersignal.

Optionally, it is also possible for the coupling conductor element 2 tobe arranged in a movable manner and the conductor element 1 to bearranged in a stationary manner.

FIG. 6 shows a block diagram of a device with a stationary coaxialconductor element 1. A radiofrequency carrier signal modulated by thedata signal is fed into the conductor element 1 at the first end thereofby means of the radiofrequency transmission unit 3. The conductorelement 1 has an embodiment in accordance with FIG. 2 and is provided atthe second end thereof with a termination 19 for a reflection-freetermination.

One coupling conductor element 2, embodied in accordance with FIG. 2, isarranged along the conductor element 1 for the purposes of decouplingthe radiofrequency carrier signal from the first conductor element 1.The coupling conductor element 2 is preferably a few wavelengths (a fewcm) long and terminated by a termination 19 at the first end thereof. Aradiofrequency reception unit 4 is connected at the second end thereofand receives and demodulates the decoupled radiofrequency carriersignal.

FIG. 7 shows a computed tomography system according to the invention,comprising a stationary gantry part 13, in which a rotatable gantry part12 is situated, with two x-ray tubes 14 and two x-ray detectors 15 beingarranged thereon. For examination purposes, a patient 16 is introducedinto a measurement field with the aid of a patient couch 20 which isdisplaceable along a system axis 17 such that an absorption of the x-rayradiation can be measured from different projection angles. A computer18, which is configured as a control and computational unit, serves tocontrol the system. Computer programs which carry out a control of thecomputed tomography system and an evaluation of the measured data, andalso a reconstruction of the desired tomographic image data, areexecuted on the computer 18.

It is necessary to transfer a large amount of arising data in acontactless manner, in particular when transferring the detector datafrom the two detectors 15 on the rotatable gantry part 12. To this end,a device according to the invention in accordance with FIG. 1 to FIG. 4for contactless transfer of electrical signals is attached to therotatable gantry part 12 and the stationary gantry part 13 such thatsaid signals can be transferred between the two gantry parts 12 and 13which are rotatable in relation to one another.

Also, there can be a data transfer with a device according to FIG. 5 orFIG. 6 for the purposes of controlling patient tables in imaging medicalengineering systems. List of reference signs

-   1 Coaxial conductor element-   2 Coaxial coupling conductor element-   3 Radiofrequency transmission unit-   4 Radiofrequency reception unit-   5 Dielectric-   6 First carrier element-   7 Second carrier element-   8 First outer conductor-   9 First inner conductor-   10 Second outer conductor-   11 Second inner conductor-   12 Rotatable gantry part-   13 Stationary gantry part-   14 X-ray tube-   15 X-ray detector-   16 Patient-   17 System axis-   18 Computer-   19 Termination-   20 Air gap-   21 Field lines-   22 Direction of rotation-   23 Movement direction-   24 Patient couch

1. A computed tomography system with a contactless data signal transfer,comprising: at least one longitudinally slit coaxial conductor element(1), at least one radiofrequency transmission unit (3) which feeds aradiofrequency carrier signal, modulated with a data signal to betransferred, into the conductor element (1), at least one longitudinallyslit coaxial coupling conductor element (2) which is embodied to receivethe emitted modulated radiofrequency carrier signal (21) from the nearfield of the coaxial conductor element (1), at least one radiofrequencyreception unit (4) which is electrically connected to the couplingconductor element (2) and embodied to extract the data signal from thereceived modulated radiofrequency carrier signal, a first gantry part(12) arranged in a rotatable manner, on which the coaxial conductorelement (1) is arranged in a circular-ring-shaped manner, and a secondgantry part (13) arranged in a stationary manner, on which the couplingconductor element (2) is arranged.
 2. A computed tomography system witha contactless data signal transfer, comprising: at least onelongitudinally slit coaxial conductor element (1), at least oneradiofrequency transmission unit (3) which feeds a radiofrequencycarrier signal, modulated with a data signal to be transferred, into theconductor element (1), at least one longitudinally slit coaxial couplingconductor element (2) which is embodied to receive the emitted modulatedradiofrequency carrier signal (21) from the near field of the coaxialconductor element (1), at least one radiofrequency reception unit (4)which is electrically connected to the coupling conductor element (2)and embodied to extract the data signal from the received modulatedradiofrequency carrier signal, a first gantry part (12) arranged in arotatable manner, on which the coupling conductor element (2) isarranged, and a second gantry part (13) arranged in a stationary manner,on which the coaxial conductor element (1) is arranged in acircular-ring-shaped manner.
 3. A patient table for imaging medicalengineering systems with a contactless data signal transfer, comprising:at least one longitudinally slit coaxial conductor element (1), at leastone radiofrequency transmission unit (3) which feeds a radiofrequencycarrier signal, modulated with a data signal to be transferred, into theconductor element (1), at least one longitudinally slit coaxial couplingconductor element (2) which is embodied to receive the emitted modulatedradiofrequency carrier signal (21) from the near field of the coaxialconductor element (1), at least one radiofrequency reception unit (4)which is electrically connected to the coupling conductor element (2)and embodied to extract the data signal from the received modulatedradiofrequency carrier signal, wherein the conductor element (1) and thecoupling conductor element (2) are movably arranged relative to oneanother in a translational manner.
 4. The device as claimed in one ofclaims 1 to 3, characterized in that the frequency of the radiofrequencycarrier signal is greater than 10 GHz.
 5. The device as claimed in oneof the preceding claims, characterized by a first carrier element (6),in which the coaxial conductor element (1) is formed.
 6. The device asclaimed in claim 5, characterized in that the first carrier element (6)is made of metal and forms a first outer conductor (8) of the coaxialconductor element (1).
 7. The device as claimed in claim 6,characterized in that the first carrier element (6) has a rectangularcross section and a first inner conductor (9) is arranged in a groove ofthe first carrier element.
 8. The device as claimed in one of thepreceding claims, characterized by: a second carrier element (7), inwhich the coaxial coupling conductor element (2) is formed.
 9. Thedevice as claimed in claim 8, characterized in that the second carrierelement (7) is made of metal and forms a second outer conductor (10) ofthe coaxial coupling conductor element (2).
 10. The device as claimed inclaim 9, characterized in that the second carrier element (7) has arectangular cross section and the second inner conductor (11) isarranged in a groove of the second carrier element (7).